a) Field of the Invention
The invention concerns a thermally controlled valve provided in the cooling water system of an internal combustion engine. In particular, the present invention concerns a thermally controlled valve located between an engine and a radiator for regulating the flow of cooling water therebetween. A thermally controlled valve according to the present includes a valve stem which is relatively movable with respect to a valve seat. The relative movement is controlled by thermal expansion and contraction of a moving unit in response to temperature changes of the cooling water.
b) Description of Related Art
FIG. 1 schematically illustrates a conventional arrangement including a water jacket 2 through which cooling water circulates around the cylinders of an engine block 1. The water jacket 2 is connected to a radiator 3 by passageways 4.sub.1 and 4.sub.2. A water pump 5 for circulating the cooling water is positioned proximate to a inlet 2a to the water jacket 2. A cooling water bypass 4.sub.3 is provided between the cooling water passageways 4.sub.1 and 4.sub.2. A thermally controlled valve TS' is provided in passageway 4.sub.1 through which cooling water is moved from the outlet of the water jacket 2 to the inlet of the radiator 3. Circulation of the cooling water is regulated by the thermally controlled valve TS'.
Operation of the thermally controlled valve TS' located in passageway 4.sub.1 of the conventional arrangement is influenced not only by the temperature, but also the pressure of the cooling water (i.e. the discharge pressure of the water pump in addition to the vapor pressure). Consequently, delays occur in opening the conventional valve TS' even though the specified temperature for operating the thermally controlled valve TS' is surpassed. Additionally, the conventional valve TS' instantaneously goes from a completely closed position to a fully open position when the specified operating temperature is surpassed.
In the aforementioned conventional arrangement, the phenomenon known as "overshoot" occurs when the valve TS' suddenly opens and cool water in the radiator surges into the water jacket 2 thereby lowering the cooling water temperature below the operating temperature of the valve TS'. In response, the valve TS' shuts immediately. This phenomenon is known as "undershoot". Repeated overshoot and undershoot cause thermal hunting, or vacillation, which in turn causes instability in the temperature of the water jacket 2.
Unstable temperatures in the water jacket 2 reduce the service life of the engine, as well as deteriorate the fuel economy of the engine. Additionally, fluctuations in the temperature of the water jacket 2 adversely affect the climate control systems for the vehicle and, in vehicles equipped with cooling water temperature gauges, cause the driver to misinterpret the status of the cooling system.
FIG. 2 shows a conventional vertical two-stage thermally controlled valve TS' which reduces thermal hunting by reducing the surge of cool water from the radiator 3, i.e. reducing the initial flow rate of cooling water. Conventional thermally controlled valve TS' includes a thermo-element TH, a case 6, and a thermally expanding unit 7 which relies on thermal expansion/contraction of a mixture of paraffin and copper powder housed in the case 6. Conventional valve TS' further includes a diaphragm 8 made of nitrile rubber, for example, to seal the thermally expanding unit 7 within the case 6, and a guide cylinder 9 connected with the opening into the case 6 sealed by the diaphragm 8. The guide cylinder 9 includes, in succession from the diaphragm 8, a fluid 10, a rubber piston 11, a back-up plate 12 made of poly-tera fluoro-ethylene (PTFE), for example, and a moving unit piston 13. Additionally, the valve TS' includes a valve seat body 14, and a support unit 15 mounted on top of the valve seat body 14 and which pushes on the moving unit piston 13 via a spring (unnumbered). A flange 14a of the valve seat body 14 is fastened to an interior surface 17a of an elastic ring 17 having sealing projections 16.sub.1, 16.sub.2 and 16.sub.3 on the upper, lower and radially outer surfaces, respectively. The elastic ring 17 is set in a corresponding housing of the passageway 4.sub.1 so as to mount the thermally controlled valve TS'. The valve TS' further includes a valve seat 14b proximate to the flange 14a of the valve seat body 14.
A first valve element 18 having a radially inner surface is slidably supported on the guide cylinder 9 of the thermo-element TH, a radially outer surface 18a of the first valve element 18 is adapted to contact the valve seat 14b, a plurality of circulation holes 18b are proximate to the radially inner surface of the first valve element 18, and a bottom surface 18c of the first valve element 18 which is proximate to the circulation holes 18b contacts a top surface of 6a of the case 6.
A second valve element 19 functions as a rigid pushing plate. A radially inner surface 19b of the second valve element 19 is fixed to the guide cylinder 9 of the thermo-element TH, and a radially outer surface 19a of the second valve element 19 is spaced from and faces a planar top surface 18d of first valve element 18. A circulation hole 19d is radially spaced between the outer surface 19a and the inner surface 19b.
A first spring 20 is mounted in compression between the second valve element 19 and the first valve element 18. A second spring 21 is mounted in compression between the first valve element 18 and a frame 22 fixed to the bottom side of the flange 14a of the valve seat body 14.
A guide hole 22a is formed in a lower portion of the frame 22. The case 6 of the thermally controlled valve TH is slidably supported in the guide hole 22a.
A third valve element 25 is slidably supported on extension 23 from the bottom of the case 6 of the thermally controlled valve TH. A stopper 24 at the tip of the extension 23 retains the third valve element 25 on the extension 23. A third spring 26 is mounted in compression between the third valve element 25 and the case 6 of the thermally controlled valve TH. The third spring 26 pushes the third valve element 25 toward a valve seat 27 formed by the cooling water bypass 4.sub.3.
The function of the vertical 2-stage thermally controlled valve TS' will now be described. When the temperature of the cooling water increases, the thermally expanding unit 7 in the thermally controlled valve TH expands (FIG. 3A). The moving unit 13, fixed with respect to the supporting unit 15, provides a reaction member against which the thermo element TH is displaced. The second valve element 19, fixed with respect to the guide cylinder 9, is also displaced so as to separate the tip 6a of the case 6, also fixed with respect to the guide cylinder 9, from the bottom 18c of the first valve element 18.
Initially a small amount of cooling water flows as indicated by arrow "a" through the gap between tip 6a and the bottom 18c. the circulation hole 18b, and circulation hole 19d.
As the temperature of the cooling water further increases, the thermally expanding unit 7 continues to expand against the moving unit 13 so as to further displace the guide cylinder 9 and the case 6. Subsequently, the outer circumferential surface 19a of the second valve element 19, fixed with respect to the guide cylinder 9, pushing against the planar surface 18d of the first valve element 18 separates the outer circumferential surface 18a of the first valve element 18 from the valve seat 14b. This allows the cooling water to flow not only as indicated by arrow "a", but also through the gap between the valve seat 14b and the outer circumferential surface 18a, as indicated by arrow "b".
As described above, a small amount of water is designed to flow initially as the temperature increases. This prevents a large amount of cold water from flowing immediately, thereby reducing thermal hunting.
Inasmuch as reference numerals are consistently used to identify corresponding elements described with respect to the aforementioned conventional vertical 2-stage type thermally controlled valve, the description of these elements will not be repeated herein.
FIGS. 4-6 illustrate another conventional thermally controlled valve having a sub-valve to reduce thermal hunting. A main valve TS.sub.1 and a thermo-element TH.sub.1, similar to the above valve TS' and thermo-element TH, are mounted eccentrically from the center of the valve seat 14 (toward the right in FIG. 4). A sub-valve or a sub-thermally controlled valve TS.sub.2, including a thermo-element TH.sub.2 used in the sub-thermally controlled valve TS.sub.2, are mounted eccentrically from the center of the valve seat 14 (toward the left in FIG. 4). The sub-thermally controlled valve TS.sub.2 has nearly an identical structure to that of TS' and TS.sub.1.
Differences between the main thermally controlled valve TS.sub.1 and the sub-thermally controlled valve TS.sub.2 include:
1) the tip end of the moving unit 13 in the thermo-element TH.sub.2 is held eccentrically from the center of the valve seat body 14 by a supporting unit 28; PA1 2) the guide cylinder 9 has a smaller diameter at an upper portion 9a and a larger diameter at a lower portion 9b; PA1 3) a circulation passageway 29 is formed between the upper portion 9a and the holding unit 2; and, PA1 4) a spring plate 31 biases the lower portion 9b into contact with a valve seat 30, thereby closing the passageway 29.
The operation of the thermally controlled valve having a sub-valve as illustrated in FIGS. 4 and 5 will now be described. As shown in FIG. 6(A), an increase in cooling water temperature causes the thermally expanding unit 7 of the thermo-element TH.sub.2 to expand. The moving unit 13, fixed with respect to the supporting unit 28, provides a reaction member against which the thermo-element TH.sub.2 is displaced. This displaces the guide cylinder 9 such that the lower portion 9b separates from the valve seat 30, whereupon the cooling water flows through the circulation passageway 29 as indicated by arrow "a".
FIG. 6(B) shows that as the temperature of the cooling water further increases, the thermally expanding unit 7 in the thermo-element TH.sub.1 expands against the moving unit 13 so as to further displace the guide cylinder 9. Subsequently, the first valve element 18 fastened to the guide cylinder 9 is separated from the valve seat 14b, against the opposition of the spring 21. This allows the cooling water to flow not only through the circulation passageway 29, as indicated by arrow "a", but also through the gap between the valve seat 14b and the first valve element 18, as indicated by arrow "b".
As set forth above, the sub-valve is first opened with an initial increase in the temperature of cooling water to allow a small amount of water to flow between the radiator and the engine. Consequently, a large amount of the cold water is prevented from flowing immediately after the valve is actuated, and thermal hunting is reduced.
The vertical 2-stage thermally controlled valve shown in FIGS. 2 and 3, or the thermally controlled valve having a sub-valve shown in FIGS. 4-6 reduce thermal hunting. However, these conventional valves include many parts which have to be assembled. Because the structures are fairly complex, production of the conventional valves is costly, and the valves are susceptible to failure. Additionally, conventional two-stage valves are also heavier than thermally controlled valves having a single stage.